1. Field of the Invention
The field of this invention relates to registration devices used for positioning work pieces on a worktable and holding the same in place while the work piece is operated on. More particularly, this invention relates to registration devices that are attached to the tooling plate of the work tables of numeric controlled machine tools to register printed circuit boards and other work pieces for drilling or other machine operations.
2. Description of the Related Art
Printed Circuit Board (PCB) drilling machines are typically computer controlled machines having a table that moves in any X, Y plane, and a spindle that moves perpendicular to the table in the Z direction to drill holes in the PCB. One or more plates are mounted on the X, Y table, commonly called tooling plates, onto which stacks of one or more PCBs are placed. PCBs come in a variety of lengths, widths and thickness. However, PCBs always have at least two registration pins which are mounted in or through the PCB, so that the pins can be used to precisely mount the board into a known position after the board has been manually or automatically loaded onto the tooling plate. The tooling plate uses clamps and a registration bar, both of which are securely mounted on the plate, and are used to register the PCB with the drilling machine. The clamps are moving parts that are biased against the pins and hold the pins in place against the registration bar.
The registration pins are typically located at the center of two opposite edges of the PCB. In one common registration method as illustrated in FIGS. 8A and 8B, referred to as V-registration, the first registration pin 310 is held into place in a V-shaped registration block 125a at the end of a registration bar. The second pin 320, also referred to as the anti-rotation pin, is held against the registration bar by an elongated clamping bar (not shown). The registration block may be attached or separated from the registration bar. The V-shaped end of the registration bar is aligned to the drilling machine, so that the lead pin can be used as a starting dattuin for creating a drilling program for the PCB. The trailing pin is aligned with the lead pin, so that the centerline formed by the centers of the two registration pins is parallel with the registration bar.
The diameter of the registration pins is dependent on the thickness of the PCB. In use the V shaped clamping mechanism receives different diameter registration pins which occupy different positions within the V and maintain the same centers. However, different diameter pins create a problem, because different diameter registration pins can result in a misalignment of the registration pins and the anti-rotation pin leading to random registration errors. The first registration pin with the new diameter will still align its center properly in the V-shaped end of the registration bar because the V shape maintains axial alignment, but the trailing anti-rotation pin is aligned to the registration bar on one side thereof. Accordingly, the anti-rotation pin will extend away from the registration bar by its radius and not its axis, such that the centerline between the lead and trailing pins axes will be skewed so that the centerline is no longer parallel to the registration bar. The registration errors are detectable in the sub-micron level precision required for the accurate drilling of PCBs and holes will be drilled in the wrong locations.
In order to properly register the PCB with the drilling machine, the registration bar and in some cases the registration block needs to be adjusted in the tooling plate by moving in the X and Y dimension the registration block in the X and Y dimension so that the centerline formed by the two registration pins will be parallel to the registration bar. This adjustment must be made each time a different diameter registration pin is used. Because the tooling plate is heavy, and therefore difficult to move in the small distances that are required to calibrate the registration bar and the registration block with the drilling machine, a tedious, time-consuming manual alignment process that must occur whenever a PCB with a different registration pin size is loaded onto the drilling machine. If the registration block is attached to the end of the registration bar, alignment is even more difficult.
For the foregoing reasons, there is a need for a registration system that will eliminate the registration errors introduced by misalignment of the PCB when the registration pin size changes.